SPID#: 49 The two central themes in our studies of primate social behavior at the Yerkes RPRC are a) conflict resolution, and b) reciprocal altruism. Conflict resolution is investigated through observations on a variety of species. These observations follow interactions in the period immediately following spontaneous aggressive incidents. The purpose is to determine if affiliative interaction took place (defined as reconciliation if between former opponents, and consolation if a bystander contacts one of the conflict participants). In addition, a pilot study of heart-rate in free-ranging subjects is being conducted so as to add physiological stress measures to the information on post- conflict events. A small transmitter is implanted subcutaneously in a rhesus monkey so that her heart rate can be correlated with ongoing events in the group. The reciprocity studies, on the other hand, focus on food-sharing in chimpanzees and capuchin monkeys. The chimpanzee study concerns spontaneous sharing in two large compound-living groups at the Yerkes Field Station. The capuchin study is of an experimental nature, in which one monkey of a pair receives food while separated from the other by mesh. The food possessor often shares with the other through the mesh. These monkeys live normally in a social group pairs are removed for brief test periods. Both studies focus on the contingency between given and received favors, especially whether reciprocal altruism in nonhuman primates requires cognitive explanations in terms of mental record-keeping.